To effectively realize confusion and deception of decoys in ballistic missile midcourse, the movement trajectory and spatial distribution of the released decoys were studied. Based on the elliptical orbit theory, the spatial relative movement model between decoys and warhead was established, and constraint condition of decoys spatial distribution under the defense systems radar detection ability was deeply explored, then the effective spatial distribution of decoys was modeled. Through simulation analysis, the movement and the position between decoys and warhead were analyzed, and the effective spatial configuration of decoys was obtained under certain radar detection ability. The study here has certain reference values for advancing the effectiveness of ballistic missile penetration aids.